PHP Detecting if source image url link leads to a "broken" image?

Question

Suppose you have a thumbnail generator script that accepts source images in the form of a URL. Is there a way to detect if the source URL is "broken" - whether nonexistent or leads to an non-image file?

---

Just brute force using getimagesize() or another PHP GD function is not a solution, since spoofed stray URL's that might not be images at all (http://example.com/malicious.exe or the same file, but renamed as http://example.com/malicious.jpg) could be input - such cases could easily be detected by PHP before having to invoke GD. I'm looking for GD pre-sanitizing before having GD try its battalion at parsing the file.

---

as a first step, the following regular expression checks if the URL is an image extension: preg_match('@(https?://([-\w\.]+)+(:\d+)?(/([\w/_\.]*(\?\S+)?)?)?)([^\s]+(\.(?i)(jpg|png|gif|bmp))$)@', $txt,$url);

Answer 1

use file_exists function in php, you can check urls with it.

See documentation below, shows how to check img... exactly what you need

FILE EXISTS - http://www.php.net/manual/en/function.file-exists.php#93572

URL EXISTS - http://www.php.net/manual/en/function.file-exists.php#85246

---

Here is alternative code for checking the url. If you will test in browser replace \n with <br/>

<?php

$urls = array('http://www.google.com/images/logos/ps_logo2.png', 'http://www.google.com/images/logos/ps_logo2_not_exists.png');

foreach($urls as $url){
   echo "$url - ";
   echo url_exists($url) ? "Exists" : 'Not Exists';
   echo "\n\n";
}


function url_exists($url) {
    $hdrs = @get_headers($url);

    echo @$hdrs[1]."\n";

    return is_array($hdrs) ? preg_match('/^HTTP\\/\\d+\\.\\d+\\s+2\\d\\d\\s+.*$/',$hdrs[0]) : false;
}
?>

Output is as follows

http://www.google.com/images/logos/ps_logo2.png - Content-Type: image/png
Exists

http://www.google.com/images/logos/ps_logo2_not_exists.png - Content-Type: text/html; charset=UTF-8
Not Exists